Recently, a piezoelectric vibrator (package) utilizing quartz or the like has been used in a cellular phone and a portable information terminal as the time source, the timing source of a control signal, a reference signal source, and the like. The piezoelectric vibrator of this type is proposed in a variety of forms, and an SMD-type piezoelectric vibrator is one example. The SMD-type piezoelectric vibrator includes, for example, a base board and a lid board which are bonded to each other, a cavity formed between the two boards, and a piezoelectric vibrating reed (electronic component) accommodated in a state of being airtightly sealed in the cavity.
In addition, in the manufacturing process of the piezoelectric vibrator, there is known a technique in which a bonding film is formed on a lower surface of the lid board (a bonding surface to be bonded to the base board) when the lid board is bonded to the base board, and the base board and the lid board are anodically bonded using the bonding film. Specifically, the two boards are heated in a state of being superimposed onto each other, and a voltage is applied to the bonding film. By doing so, an electrochemical reaction occurs at an interface between the bonding film and the base board, whereby the two boards can be closely adhered tightly.
However, in the described piezoelectric vibrator, when the piezoelectric vibrator is heated, for example, during the anodic bonding of the lid board and the base board, outgas (for example, oxygen) is discharged into the cavity. When the outgas is present in the cavity, the degree of vacuum in the cavity decreases, and an equivalent resistance value (effective resistance value Re) increases. As a result, there is a problem in that the drive voltage of the piezoelectric vibrator increases, and thus energy efficiency decreases.
As a method of increasing the degree of vacuum in the cavity and suppressing the equivalent resistance value, gettering is known, for example. Gettering is a method of disposing a metal film in the cavity as a gettering material, heating the gettering material to be activated, thus absorbing outgas present in the cavity by a chemical reaction of the gettering material. For example, JP-A-2006-86585 discloses a configuration in which a bonding film is formed on the entire surface of the lid board facing the base board, and a gettering material made, for example, of magnesium is contained in the bonding film. According to this configuration, by heating the bonding film containing the gettering material with electron beams, or the like when the lid board and the base board are bonded together, the bonding film is melted, so that the lid board is bonded to the base board, and outgas discharged into the cavity during the bonding can be absorbed by the gettering material.
However, the configuration disclosed in JP-A-2006-86585 has a problem in that it is difficult to increase sufficiently the degree of vacuum in the cavity. That is to say, in the configuration disclosed in JP-A-2006-86585, since the gettering material is contained in the bonding film, the outgas will be discharged from the bonding film at the same time as the gettering. For this reason, there is a problem in that it is difficult to absorb the outgas discharged from the bonding film immediately before the end of the gettering and during periods after the end of the gettering until the temperature of the piezoelectric vibrator decreases.
To solve the problems, a method in which before bonding the lid board and the base board, the bonding film is heated to a high temperature in advance to preliminarily discharge the outgas from the bonding film, and then the lid board and the base board are bonded together may be considered. However, according to this method, since the gettering material will be degraded before bonding the lid board and the base board, there is a problem in that it is difficult to absorb the outgas present in the cavity after bonding.